While walking around Paris for the last month, I’ve been fascinated by the highly fossiliferous limestone that comprises so many of its iconic structures. At one point I thought, Hmm… The City of Light is built with materials of death. I had no idea how much farther that thought would take me.

Without abundant death we wouldn’t have asphalt, concrete, marble, travertine, chert, oil, coal or countless other graces of civilization. Still, there seemed to be an unusual abundance of limestone in use here, and I wondered where it came from. Naturally, from my 21st century perspective, I assumed that all the stone had been quarried in some other place: hills outside of town, perhaps. (Lutetian limestone, it’s called, and it’s a relatively new rock: only only a few dozen million years old. Younger than dinosaurs. It’s also known as “Paris stone”, and has become quite the fashion item lately.) What I hadn’t figured was that nearly all of this building stone, for many centuries, was extracted from beneath Paris itself.

I didn’t learn that fact until we visited the Catacombes a couple days ago.

The Catacombes are bone banks called ossuaries. They occupy abandoned quarries beneath Paris and contain the remains of more than six million people. Many of the deceased are surely the same men (and women? probably) who carved out the quarries, mostly in the first several centuries of the last millennium. It must have been quite a project, since they withdrew enough rock to assemble Notre Dame, thousands of other churches large and small, bridges, city walls and homes — and left beneath the streets of Paris more than 300 kilometers (100 miles) of tunnels, including rooms and vaults that together comprise a vast man-made cave system. Top to bottom, a vertical cross-section of Paris looks like this:

Surface — streets, buildings, parks

Metro tunnels

Sewers

Quarries

Fossils are bones of stone, I explained to my kid. And limestones are stones of bone. Here in the Catacombes, down hallways that go on and on and on and on, the bones of dead Parisians are stacked into walls, with an artistry that makes one wonder what was going on in the heads of the masons. The walls facing the halls and passing visitors are built mostly with femurs and skulls. The femurs are stacked and interlocked, with the knee knuckles outward, course after course forming a pattern like stitches in a cloth. These are interrupted by horizontal lines of skulls, and usually topped with a final row: a crowning course of human heads. Here and there some arm bones might be used, but femurs and skulls were clearly the preferable building material. Behind these walls behind lie the rest of the bones: remains of remains.

The masons were priests. The bones were gathered from the city’s cemeteries, which had become rotten with an abundance of corpses as the end of the 18th century approached. That’s when it was decided to move the bones down into deeper graves. The quarries were empty, so the bones came down. The whole project went in stages, running from the late 1700s to the middle 1800s. The priests, whose jobs already required exceptional respect for the dead, were conscripted for the work.

The pictures in my collection (such as the one above) aren’t the best I’ve taken. Most of the light was provided by dim illumination in the catacombes itself, or by cell phones. If you wish to know more (and I recommend it), here are a pile of fascinating links:

Since one walks through the tunnels in the company of others, it is less creepy than you might think. After a while, endless aisles of bones also tend to make the bones themselves ordinary. Yet one wonders: Is this skull Robespierre’s? Danton’s? Both lost their heads at the guillotine, but down here all heads are equally ordinary and anonymous, fully respected, but still just building material.

A lesson: different as we all are in life, we are remarkably identical in death. Skulls tend to all look the same. So do other bones. One can say, These were babies once. Then laughing children. They grew up, learned about life, and lived long enough to produce more babies and get work done. And what they’ve left is no different than what everybody else leaves.

What makes us animals is that we eat other living things. (We need their carbon.) We live on things that lived. And we build with them too. Death supplies us. In turn, we supply as well. And all our turns will come.

What makes us different is who and what we are, and what we do, when we’re alive. Life is for the living. And so, it turns out, is death.